Many steroid hormones are biliary excreted, metabolized in an orderly and systematic fashion by the intestinal flora, reabsorbed, conjugated in the liver, and excreted in the urine. Thus, the metabolism of these hormones by the intestinal bacteria is a normal, physiological function throughout life. As the only laboratory studying the transforming bacterial species we have established the bacterially mediated pathways of most corticoids and isolated and identified the organisms involved. The bacteria metabolizing aldosterone, 17 alpha-OH corticoids, and sex hormones undergoing enterohepatic circulation are unknown as are the metabolic pathways of these structures. We propose to isolate and identify the bacteria responsible for 21-dehydroxylation of aldosterone, for the transformation of 17 alpha-OH corticoids to androgens (desmolase activity), for conversion of 16 alpha-hydroxyprogesterone to 17 alpha-pregnanolone, for the conversion of 16 alpha-hydroxyestrone to the 15 alpha-structure, and for the aromatization of androstenedion. Intermediary and final metabolites will be isolated and identified, and the metabolic pathways will be determined. The environmental requirements of the organisms (Eh and pH) performing the specific alterations will be examined with a view to assess the likelihood that the transformations take place in the human gut.